Flexible circuit board, folding screen and display module

Abstract

The utility model relates to the technical field of circuit boards, in particular to a flexible circuit board, a folding screen and a display module. The flexible circuit board comprises a composite circuit substrate and a reinforcing sheet, the composite circuit substrate comprises a to-be-bent part and a non-bent part which are connected in the length direction, the non-bent part is arranged at the two ends of the to-be-bent part, and the composite circuit substrate comprises a first surface and a second surface which are oppositely arranged in the thickness direction. The to-be-bent part is configured to deform, so that at least part of the second surface is located on the outer side of the first surface; the composite circuit substrate is internally provided with an air gap area, and the air gap area is located at a to-be-bent part and at least a part of a non-bent part. The flexible circuit board further comprises a reinforcing sheet, the reinforcing sheet is installed on the first surface of the non-bending part, and the projection of the reinforcing sheet in the thickness direction of the flexible circuit board falls in the air gap area. According to the flexible circuit board, the bending reliability of the flexible circuit board can be enhanced through the reinforcing sheet.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of circuit board, in particular to a flexible circuit board, a foldable screen and a display module. BACKGROUND

[0002] Flexible Printed Circuit (FPC) is also called flexible circuit board, soft circuit board, soft board, etc. It is a special printed circuit board with the characteristics of light weight, thin thickness, softness and bendability. With the rapid development and application of foldable screen mobile phones and other electronic devices, flexible circuit boards are increasingly used due to their high flexibility and resistance to repeated bending, and have become an important and indispensable component. In order to improve the bending reliability of the flexible printed circuit board in the foldable screen product, an Airgap structure design is usually adopted, i.e. an air gap structure. Airgap can improve the flexibility of the to-be-bent part, thereby increasing the bending reliability.

[0003] However, the design of the Airgap region will cause the inner side of the flexible printed circuit board to bulge and protrude during the bending process, resulting in a large stress on the copper foil in the protruding region. In addition, when applied to the bending of the foldable screen, the protrusion is easy to touch other components of the foldable screen, further increasing the stress on the copper foil and increasing the risk of copper foil failure. CONTENT OF THE INVENTION

[0004] In view of this, in order to solve the above problems, the present application provides a flexible circuit board, a foldable screen and a display module.

[0005] In a first aspect, the present application provides a flexible circuit board, comprising a composite circuit substrate and a reinforcing sheet. The composite circuit substrate comprises a to-be-bent part and a non-bending part connected along the length direction. The non-bending part is arranged at both ends of the to-be-bent part. The composite circuit substrate comprises a first surface and a second surface arranged oppositely along the thickness direction. The to-be-bent part is configured to deform so that at least part of the second surface is located outside the first surface. An air gap region is arranged inside the composite circuit substrate. The air gap region is located in the to-be-bent part and at least part of the non-bending part. The reinforcing sheet is mounted on the first surface of the non-bending part. The projection of the reinforcing sheet along the thickness direction of the flexible circuit board falls within the air gap region.

[0006] By arranging the reinforcing sheet, the strength of the target region can be increased, the protrusion height of the target region during bending can be reduced, the contact between the target region of the flexible circuit board and the surrounding components can be alleviated, the deformation and contact stress of the copper foil in the target region can be reduced, the risk of copper foil failure can be reduced, and the bending reliability of the flexible circuit board during work can be improved.

[0007] In some embodiments, along the length direction of the flexible circuit board, the horizontal distance between the center of the reinforcing sheet and the edge of the air gap region is B, the length of the air gap region is A, and 0.1A≤B≤0.3A.

[0008] The length of the air gap region is A, the horizontal distance between the center of the reinforcing sheet and the edge of the air gap region is B, and the relationship between the two satisfies: 0.1A≤B≤0.3A, which can ensure that the installation position of the reinforcing sheet is the target region.

[0009] In some embodiments, the composite circuit board includes a first circuit board, a first adhesive layer, and a second circuit board which are sequentially stacked, the first adhesive layer connects the first circuit board and the second circuit board, the surface of the first circuit board away from the first adhesive layer is a first surface, and the surface of the second circuit board away from the first adhesive layer is a second surface; the air gap region is formed in the first adhesive layer.

[0010] The air gap region is formed in the middle region of the composite circuit board, and the stress of each part is more uniform when the flexible circuit board is bent.

[0011] In some embodiments, at least one of the first circuit board and the second circuit board includes a first dielectric layer, a conductive layer, a second adhesive layer, and a second dielectric layer which are sequentially stacked, and the first circuit board and the second circuit board are connected through the first dielectric layer and the first adhesive layer.

[0012] When viewed from the direction of the first adhesive layer pointing to the first surface or the second surface, the first dielectric layer, the conductive layer, the second adhesive layer, and the second dielectric layer sequentially move away from the first adhesive layer.

[0013] In some embodiments, the air gap region is also provided in the second adhesive layer.

[0014] The air gap region is provided on the second adhesive layer, and the multi-layer of the prepared flexible circuit board contains the air gap region, and the flexibility of the flexible circuit board is better.

[0015] In some embodiments, at least one of the first circuit board and the second circuit board is a single-sided circuit board.

[0016] The single-sided circuit board is used as the first circuit board or the second circuit board, the production process of the flexible circuit board is relatively simple, and the manufacturing cost is low.

[0017] In some embodiments, the reinforcing sheet and the non-bending part are adhesively connected.

[0018] The reinforcing sheet and the composite circuit board are connected by adhesion, and the installation process of the reinforcing sheet is simple.

[0019] In a second aspect, the present application provides a folding screen, comprising the flexible circuit board according to any one of the first aspect.

[0020] In a third aspect, the present application provides a display module, comprising the folding screen according to the second aspect. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 A structural schematic diagram of the flexible circuit board provided by the present application.

[0022] Figure 2 A structural schematic diagram of the flexible circuit board provided by the present application. Figure 1 A structural schematic diagram of the flexible circuit board provided by the present application.

[0023] Explanation of main element symbols:

[0024] I, to be bent part; II, non-bent part; III, air gap region;

[0025] 10, composite circuit board; 2, first surface; 3, second surface; 4, first circuit board; 41, first dielectric layer; 42, conductive layer; 43, second adhesive layer; 44, second dielectric layer; 5, first adhesive layer; 51, first hollow part; 6, second circuit board;

[0026] 20, reinforcing sheet. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments.

[0028] Flexible printed circuit board (FPC) is also known as flexible circuit board, soft circuit board, soft board, etc. It is a special printed circuit board with the characteristics of light weight, thin thickness, softness and bendability. With the rapid development and application of folding screen mobile phones and other electronic devices, flexible circuit boards are increasingly used due to their high flexibility and repeated bending resistance, and have become an important and indispensable component. In order to improve the bending reliability of flexible printed circuit boards in folding screen products, Airgap structure design, i.e. air gap structure, is usually used. Airgap can improve the flexibility of the to-be-bent part, thereby increasing the bending reliability.

[0029] However, the design of the Airgap area causes bulges to appear on the inside of the flexible printed circuit board during bending, resulting in greater stress on the copper foil in the bulging area. At the same time, when applied to the bending of a foldable screen, this bulge is prone to contact with other components of the foldable screen, generating friction and contact stress in the bulging area, further increasing the stress on the copper foil and increasing the risk of copper foil failure.

[0030] In view of this, this application provides a flexible circuit board, please refer to... Figure 1 and Figure 2 The flexible circuit board includes a composite circuit substrate 10 and a reinforcing sheet 20. The composite circuit substrate 10 includes a bendable portion I and a non-bending portion II connected along the length direction. The non-bending portion II is disposed at both ends of the bendable portion I. The composite circuit substrate 10 includes a first surface 2 and a second surface 3 disposed opposite to each other along the thickness direction. The bendable portion I is configured to deform such that at least a portion of the second surface 3 is located outside the first surface 2. An air gap region III is provided inside the composite circuit substrate 10. The air gap region III is located between the bendable portion I and at least a portion of the non-bending portion II. The reinforcing sheet 20 is mounted on the first surface 2 of the non-bending portion II, and the projection of the reinforcing sheet 20 along the thickness direction of the flexible circuit board falls within the air gap region III.

[0031] By setting the reinforcing piece 20, the strength of the target area can be increased, and the bulge height of the target area can be reduced during bending. This reduces the contact between the target area of ​​the flexible circuit board and surrounding components, reduces the deformation and contact stress of the copper foil in the target area, reduces the risk of copper foil failure, and improves the reliability of the flexible circuit board during bending.

[0032] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the embodiments and features described below can be combined with each other.

[0033] In some implementations, the flexible circuit board is used in a foldable screen, which is used in the display module of an electronic device. The electronic device includes, but is not limited to, mobile phones, laptops, PDAs, digital cameras, and LCD screens. The selection can be made according to actual needs and is not limited here.

[0034] In some embodiments, the flexible circuit board includes a composite circuit board 10, which includes a bendable portion I and a non-bending portion II connected along its length. The non-bending portion II is disposed at both ends of the bendable portion I along its length, i.e., when viewed along the length of the composite circuit board 10, it presents an arrangement of non-bending portion II, bendable portion I, and non-bending portion II. (Understood, please continue to refer to...) Figure 2When the flexible circuit board is bent into a U-shaped structure, the to-be-bent part I forms the arc-shaped bottom of the U-shaped structure, and the non-bent part II forms the linear extension part of the U-shaped structure. The length of the to-be-bent part I and the non-bent part II can be selected according to actual needs, which is not limited here.

[0035] Further, the composite circuit board 10 further comprises a first surface 2 and a second surface 3 arranged opposite in the thickness direction. When the composite circuit board 10 is deformed, at least part of the second surface 3 is located outside the first surface 2. It can be understood that please continue to refer to Figure 2 When the flexible circuit board is bent into a U-shaped structure, the first surface 2 forms the inner wall surface of the U-shaped structure, and the second surface 3 forms the outer surface of the U-shaped structure, that is, during the bending process of the flexible circuit board, the protruding target area is located on the first surface 2 of the composite circuit board 10.

[0036] The composite circuit board 10 is formed by stacking multiple layers, specifically, a first circuit board 4, a first adhesive layer 5 and a second circuit board 6 are sequentially stacked, wherein the surface of the first circuit board 4 away from the first adhesive layer 5 is the first surface 2, and the surface of the second circuit board 6 away from the first adhesive layer 5 is the second surface 3, that is, after the composite circuit board 10 is bent, the first circuit board 4 constitutes the inside of the U-shaped structure, and the second circuit board 6 constitutes the outside of the U-shaped structure. At least one of the first circuit board 4 and the second circuit board 6 comprises a first dielectric layer 41, a conductive layer 42, a second adhesive layer 43 and a second dielectric layer 44 which are sequentially stacked, and the first circuit board 4 and the second circuit board 6 are connected by the first dielectric layer 41 and the first adhesive layer 5. It can be understood that from the direction of the first adhesive layer 5 pointing to the first surface 2 or the second surface 3, the first dielectric layer 41, the conductive layer 42, the second adhesive layer 43 and the second dielectric layer 44 are sequentially away from the first adhesive layer 5. Among them:

[0037] The first dielectric layer 41 and the second dielectric layer 44 can play the role of electrical insulation and mechanical support, ensure that short circuit does not occur between different conductive paths, and provide necessary physical support for the flexible circuit board, so that the flexible circuit board can remain intact without damage when bending or folding. They can be one of epoxy resin dielectric layer, polypropylene dielectric layer, BT resin dielectric layer, polyphenylene ether dielectric layer, polyimide dielectric layer, polyethylene terephthalate dielectric layer and polyethylene naphthalate dielectric layer, etc. They can be selected according to actual needs, which is not limited here.

[0038] The conductive layer 42 is used to carry current and transmit electrical signals, meet the needs of power distribution, and realize electrical signal transmission between various components inside the electronic device, which can be a copper wire layer, a silver wire layer, or an aluminum wire layer, etc., which can be selected according to actual needs, and is not limited here. Optionally, the conductive layer 42 used in the present application is a copper wire layer, which has excellent conductivity and relatively low cost.

[0039] The second adhesive layer 43 is used to connect the conductive layer 42 and the second dielectric layer 44, which is an adhesive material, so that the first circuit board 4 and the second circuit board 6 can be made by pressure bonding. It can be understood that first of all, the adhesive layer can provide a stable physical connection, so that the conductive layer 42 and the second dielectric layer 44 are firmly combined together, increasing the mechanical strength of the entire flexible circuit board, so that the flexible circuit board can withstand bending or folding stress in daily use; secondly, using adhesive pressure bonding can make the production process more automated and standardized, which is beneficial to improve the production efficiency and the consistency of product quality; finally, compared with other connection methods, the structure of adhesive pressure bonding can reduce the thickness and weight of the flexible circuit board, so as to meet the demand of lightweight. The specific material of the adhesive layer can be selected according to actual needs, and is not limited here.

[0040] In some embodiments, the composite circuit board 10 is provided with an air gap region III along the length direction of the flexible circuit board, the length of the air gap region III along the length direction of the flexible circuit board is A, the air gap region III is located in the first adhesive layer 5, and the air gap region III is located between the bending part I and at least part of the non-bending part II when viewed along the length direction of the composite circuit board 10. It can be understood that at least part of the air gap region III extends to the non-bending part II, which can further increase the flexibility of the composite circuit board 10, and when forming a U-shaped structure, the transition at the connection between the arc-shaped bottom and the straight extension part is better, reducing the unevenness of deformation when bending, thereby increasing the bending reliability of the flexible circuit board. The extension length of the air gap region III in the non-bending part II is not limited in the present application, and can be selected according to the specific specifications of the flexible circuit board.

[0041] Specifically, the first adhesive layer 5 is provided with a first hollow part 51 penetrating along the thickness direction, and the first adhesive layer 5, the first circuit board 4 and the second circuit board 6 form the air gap region III, that is, the first hollow part 51 is the air gap region III. It can be understood that by providing the first hollow part 51 penetrating along the thickness direction in the first adhesive layer 5 to form the air gap region III, the forming method of the air gap region III is simpler, reducing the processing cost of the flexible circuit board.

[0042] As an optional technical solution of the present application, the second adhesive layer 43 also has the air gap region III. Specifically, the second adhesive layer 43 has a second hollow portion (not shown in the figure) penetrating along the thickness direction, and the conductive layer 42, the second adhesive layer 43 and the second dielectric layer 44 enclose the air gap region III. It can be understood that the air gap region III is provided on the second adhesive layer 43, and the multi-layer structure of the flexible circuit board prepared contains the air gap region III, and the flexibility of the flexible circuit board is better.

[0043] In some embodiments, the flexible circuit board further comprises a reinforcing sheet 20, and the reinforcing sheet 20 is mounted on the first surface 2 of the non-bending portion II, that is, the number of the reinforcing sheet 20 is two, and the projection of the reinforcing sheet 20 along the thickness direction of the flexible circuit board falls within the air gap region III; along the length direction of the flexible circuit board, the horizontal distance between the center of the reinforcing sheet 20 and the edge of the air gap region III is B, and 0.1A≤B≤0.3A. It can be understood that please continue to refer to Figure 2 When the flexible circuit board is bent to form a U-shaped structure, the two reinforcing sheets 20 are respectively located at the two straight line extending portions of the U-shaped structure and are located inside the U-shaped structure.

[0044] The mounting position of the reinforcing sheet 20 meets the above-mentioned limitation, which can ensure that the mounting position of the reinforcing sheet 20 is the target region. At this time, through the setting of the reinforcing sheet 20, the strength of the target region can be increased, the protrusion height of the target region in the bending process is reduced, so as to relieve the contact between the target region of the flexible circuit board and the surrounding components, reduce the deformation and contact stress of the copper foil conductive layer 42 in the target region, reduce the risk of failure of the copper foil conductive layer 42, and improve the bending reliability of the flexible circuit board in work.

[0045] The reinforcing sheet 20 used in the present application includes but is not limited to polyimide sheet, stainless steel sheet or ceramic sheet, etc., which can be selected according to actual needs.

[0046] In some embodiments, the reinforcing sheet 20 is a rectangular sheet. It can be understood that the rectangular reinforcing sheet 20 is more uniform in strengthening each part of the target region after installation, and does not affect the bending process of the flexible circuit board.

[0047] In some embodiments, the reinforcing sheet 20 is adhesively connected with the non-bending portion II. It can be understood that the reinforcing sheet 20 is connected with the composite circuit board 10 by adhesion, and the installation process of the reinforcing sheet 20 is simple.

[0048] In the actual application process, first, the first circuit substrate 4 and the second circuit substrate 6 are respectively manufactured, then the pure glue is punched to obtain the first adhesive layer 5 with the air gap area III, the first circuit substrate 4, the first adhesive layer 5 and the second circuit substrate 6 are laminated to obtain the composite circuit substrate 10 with the air gap area III; finally, the reinforcing sheet 20 is installed to the target area by the pure adhesive bonding method, so that the horizontal distance B between the center of the reinforcing sheet 20 and the edge of the air gap area III and the length A of the air gap area III satisfy: 0.1A≤B≤0.3A.

[0049] It should be noted that the thickness of the first dielectric layer 41, the conductive layer 42, the second adhesive layer 43, the second dielectric layer 44 and the first adhesive layer 5 is not limited in the present application, and can be selected according to the production requirements of the flexible circuit board, and the length, width, thickness and number of the air gap area III can be adjusted according to the size requirements of the flexible circuit board, the number of the air gap area III can be one or more, and the number of the reinforcing sheet 20 can be multiple.

[0050] In addition, those skilled in the art should recognize that the above embodiments are only used to illustrate the present application, and are not used as a limitation on the present application, and any appropriate changes and variations made to the above embodiments fall within the scope of the disclosure of the present application.

Claims

1. A flexible wiring board comprising a composite wiring substrate including a to-be-bent portion and non-bent portions connected along a length direction, the non-bent portions being provided at both ends of the to-be-bent portion, and the composite wiring substrate including a first surface and a second surface provided opposite along a thickness direction, the to-be-bent portion being configured to be deformed so that at least a part of the second surface is located outside the first surface. The composite circuit substrate is internally provided with an air gap region, the air gap region being located at the to-be-bent portion and at least part of the non-bent portion; The flexible circuit board further comprises a reinforcing sheet, the reinforcing sheet being mounted on the first surface of the non-bent portion, and a projection of the reinforcing sheet along the thickness direction of the flexible circuit board falls within the air gap region.

2. The flexible wiring board according to claim 1, characterized by, Along the length direction of the flexible circuit board, the horizontal distance between the center of the reinforcing sheet and the edge of the air gap region is B, the length of the air gap region is A, and 0.1A≤B≤0.3A.

3. The flexible wiring board according to claim 1, characterized by The composite circuit substrate comprises a first circuit substrate, a first adhesive layer and a second circuit substrate which are sequentially stacked, the first adhesive layer connecting the first circuit substrate and the second circuit substrate, the surface of the first circuit substrate away from the first adhesive layer being a first surface, and the surface of the second circuit substrate away from the first adhesive layer being a second surface; the air gap region being formed in the first adhesive layer.

4. The flexible wiring board according to claim 3, characterized by At least one of the first circuit substrate and the second circuit substrate comprises a first dielectric layer, a conductive layer, a second adhesive layer and a second dielectric layer which are sequentially stacked, the first dielectric layer being connected with the first adhesive layer.

5. The flexible wiring board according to claim 4, characterized by The air gap region is further provided in the second adhesive layer.

6. The flexible wiring board according to claim 3, wherein At least one of the first circuit substrate and the second circuit substrate is a single-sided circuit substrate.

7. The flexible wiring board according to claim 1, wherein The reinforcing sheet comprises stainless steel material, polyimide material or ceramic material.

8. The flexible wiring board according to claim 1, characterized by The reinforcing sheet and the non-bent portion are adhesively connected.

9. A folding screen, characterized in that The foldable screen comprises the flexible circuit board according to any one of claims 1-8.

10. A display module, characterized by The foldable screen comprises the flexible circuit board according to claim 9.

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